A valve is a mechanical device by which the flow of fluid may be started, stopped, or regulated by a movable part that opens or obstructs passage. A valve may be controlled manually, pneumatically, hydraulically, mechanically, electrically, or using a combination thereof. A valve may be used for a variety of purposes, including flow control, pressure control, and directional control.
Up until now, operators of systems having one or more valves had to infer or estimate valve movement by measuring the electrical current in one or more solenoid coils associated with each valve. However, measuring the current in this way does not provide any direct data on whether the valve has actually moved. Likewise, it is impossible to tell from the current in a solenoid coil whether any fluid is actually in the valve.